1. Field of the Invention
The present invention relates to a cathode-ray tube (CRT) display device with a picture-shifting circuit and more particularly to a full-graphic display device with a picture shifting circuit.
A full-graphic display device is one which displays both words and pictures. It can display a great amount of visual data so that the operator can quickly respond to the data. For this reason, full-graphic display devices are widely used in picture-processing units, in electric power systems, in building-maintenance systems, in water supply systems, etc.
2. Description of the Prior Art
Generally, a full-graphic display device comprises a memory for storing data to be displayed to a CRT display panel, an address counter for cyclically and sequentially generating count values so as to access the memory, and a microprocessing unit for controlling data to be written into the memory or for editing data stored in the memory so as to display a desired picture. The CRT display panel and the memory have panel addresses and memory addresses, respectively. The number of memory addresses is greater than the number of panel addresses. The microprocessing unit generates reading or writing addresses, for writing data into or reading data out of the memory, and also generates offset addresses. The offset addresses are used for shifting the displayed picture on the display panel, so that the picture is shifted to the right, to the left, down, or diagonally. Rearrangement of the pic is necessary when, for example, a great amount of data is to be displayed in a simple way and at a high speed.
Conventionally, the offset addresses are calculated with other addresses by the address counter and by the microprocessing unit by using software. The use of software however, greatly delays the operating speed of the address for calculating the offset address with other addresses, counter or the operating speed of the microprocessing unit. Therefore, the conventional system involves problems in that shifting of the picture is carried out at a slow speed and in that the speed at which the microprocessing unit controls data to be written or read out of the memory is slow.